Numerous processes are know for the liquefaction of gases such as natural gas. The following are among those the most pertinent references:
U.S. Pat. No. 4,545,795 discloses a process and apparatus for liquefying natural gas using two closed cycle, multicomponent refrigerants wherein a low level refrigerant cools and liquefies the natural gas and a high level refrigerant cools and partially liquefies the low level refrigerant. The high level refrigerant is phase separated in order to use lighter refrigerant components to perform the final lowest level of refrigeration while the liquid phase of the separation is split and then expanded for refrigeration duty in order to avoid multiple flash separations wherein heavier components are used to provide the lower levels of refrigeration.
U.S. Pat. No. 4,525,195 discloses an improvement to a process and apparatus for liquefying natural gas using two closed-cycle, multicomponent refrigerants; a low level refrigerant which cools the natural gas and a high level refrigerant which cools the low level refrigerant. The improvement to the process comprising phase separating the high level refrigerant after compression and fully liquefying the vapor phase stream against external cooling fluid after additional compression.
U.S. Pat. No. 3,812,046 discloses a process for liquefaction of natural gas which employs a multicomponent cooling cycle coupled ti an absorption refrigerant cycle. The invention uses the exhaust from a driver for compressors in the multicomponent cycle to effect warming in the absorption refrigeration cycle.
U.S. Pat. No. 3,763,658 discloses a method and refrigeration system for liquefying a feed stream by first subjecting the feed stream to heat exchange with a single component refrigerant in a closed, cascade cycle and thereafter, subjecting the feed stream to heat exchange with a multicomponent refrigerant in a multiple zone heat exchanger thereby forming a second, closed refrigerant cycle.
Additional information concerning refrigeration cycles or liquefaction processes are disclosed in U.S. Pat. No. 2,826,049; 2,909,905; 3,212,276; 3,418,819 and 3,611,739.